Memphis sanitation workers protest on 29 March 1968, watched by Tennessee National Guard troops with bayonets. Martin Luther King Jr was assassinated on 4 April while in Memphis supporting the strike.
Photograph: Charlie Kelly/AP

Memphis 68: The Tragedy of Southern Soul, the second volume of an obsessively researched trilogy of histories about key years in US black “music cities”, has won its Scottish author the prestigious Penderyn music book prize.

Stuart Cosgrove was presented with the £1,000 award at the Laugharne Weekend books and music festival on Sunday, a remarkable result for a book in a trilogy that was originally intended to be self-published while its author was executive producing Channel 4’s Paralympics coverage in 2012.

A passionate fan of US soul music, Cosgrove self-published the first book in the trilogy, Detroit 67: The Year That Changed Soul, which was shortlisted for the Penderyn in 2016 and later picked up by Scottish independent publisher Polygon. Exploring the music of northern Motor City amid the foment of the civil rights struggle, the book looked at the fizzing pop invention of Motown’s golden years and the insurrectionary rumble of garage rockers such as MC5.

Memphis 68 shifts the focus to another iconic music city, home to Stax Records and musicians such as Isaac Hayes, Mahalia Jackson and Otis Redding. Set in the year of the assassination of Martin Luther King Jr, Cosgrove documents the city’s grief and anger, alongside the music that continued to resonate with the struggle for civil rights. The writer will conclude his trilogy next year with a portrait of Harlem in 1969.

Speaking to the Guardian, Cosgrove noted that white rock music has generally received much more lavish attention in music literature than black soul. “There has always been a chasm between books on rock and books on soul, which in some respects reflects the history of music journalism. In America the influence of Rolling Stone, and here in titles like the NME and Melody Maker, most of the inspired writers were from the rock legacy. I came from a very different background, from the obsessive all-nighters of the northern soul scene where there was a near religious passion for soul,” he said.

Sleaford Mods’ vocalist and judge Jason Williamson said: “The Penderyn prize introduced me to subjects and artists I wouldn’t have normally bothered with. In the case of Memphis 68 I found an old passion for soul reignited, but this time round I got an idea of its political undercurrent. Tragic, horrible, disturbing even.”